One-year monitoring of desiccation cracks in Tournemire argillite using digital image correlation

• DIC method was used for the first time in an underground gallery.
• The DIC method was used to monitor desiccation cracks during an annual climatic cycle.
• The DIC method is able to monitor clay–rock strains for at least 4 months.
• The DIC method can monitor the opening/closure of cracks for more than one year.
• Crack apertures were correlated with climatic fluctuations (RH and T).

Digital image correlation (DIC) was used for the first time in an underground gallery to monitor desiccation cracks during an annual climatic cycle. This experimental in situ investigation was carried out on a study area of 344×275 mm², located on the East96 gallery front at the Tournemire experimental station, during which the relative humidity and temperature were continuously measured for more than one year, from March 2011 to March 2012.Our results demonstrate the ability of the non-invasive DIC method to monitor clay–rock strains for at least four months, and to monitor the opening and closing of desiccation cracks for more than one year. Moreover, our study provides the following phenomenological results. As observed in the laboratory, the hydric strains were anisotropic; the strains perpendicular to the desiccation cracks were almost homogeneous and much larger than those parallel to the same cracks. The changes in crack apertures calculated from the displacement fields (at an accuracy of approximately 26.9 µm) and the strain fields were clearly correlated and concomitant with changes in relative humidity and temperature (with 25%